1. Field of the Invention
This invention relates to a tool monitor for detecting any damage to a tool of a machine tool by utilizing acoustic emissions (hereinafter referred to briefly as AE) generated at the time of occurrence of damage.
2. Discussion of the Related Art
In a machine tool such as a drilling machine, a tool such as a drill is often damaged and any such damage must be somehow detected. For the detection of such a tool damage, it is known, for instance, to install an AE sensor in contact with a machine tool near a work piece or a machine table and on a surface receiving an AE signal so that the damage to the tool may be sensed from the AE signal by the AE sensor.
However, many machine tools carry a mechanism for shifting or turning the spindle so that the machining point is often not fixed. Therefore, in such a machine, tool, the AE sensor cannot be installed in an effective position. Furthermore, even in the case of a machine tool not having a mechanism for shifting and turning the spindle, the signal level from the AE sensor varies delicately according to the condition of the propagation medium and the state of the contact surface. It is therefore difficult to select the proper position for installation of the AE sensor. In addition, it is difficult to set sensitivity properly. Moreover, machined chips may fly to the AE sensor to cause the output of an erroneous AE signal and an erratic operation of the sensor.